1. Field of the Invention
The present invention relates to a tape tracking system and, more particularly, to an active tracking system which operates to adjust the lateral position of a magnetic tape in a magnetic recorder/player to maintain the tape along a predetermined path.
2. Description of the Prior Art
An arrangement of a typical tape recorder/player is shown in FIG. 1. The device includes a pair of tape reels 10 and 12, between which and wound thereon extends a length of magnetic tape 14. The reels each includes flanges 15 and a hub 16. A number of cylindrical guide rollers 17 and capstans 18, each rotatable about its axis, are provided between the reels to define a tape path along which the tape 14 is wrapped around the guide rollers 17 and capstans 18. The orientations of the axes of the guide rollers are fixed. Several magnetic read/write heads 20 are also provided along the tape path wherein the magnetic heads 20 are disposed against the tape 14 at different lateral position across the width of the tape 14. In operation, one of the reels, for example the reel 10, rotates, for example, in a clockwise direction thereby winding the tape onto the hub 16 of the reel 10 and pulling the tape along the tape path defined by the guide rollers 17 and the capstans 18 as the tape unwinds from the reel 12. The capstans 18 regulate the precise desired tape travel speed with respect to the heads. The direction of the tape travel may be reversed by rotating the reel 12 in a counterclockwise direction.
In magnetic recording or playback, information is written onto or read from the magnetic tape 14 along individual data tracks which are of a predetermined width and are spaced laterally across the width of the magnetic tape. Each data track interacts with one magnetic head 20. In order to store greater quantities of data on the magnetic tape without having to use a wider tape, it is necessary to increase the data track density. That is, the data is stored on a greater number of tracks across the width of the tape. Therefore it is necessary to reduce the spacing between adjacent data tracks and/or the width of each data track.
As the magnetic tape travels from one reel to another along the tape path, the tape may drift laterally from a nominal path. In so doing, it moves laterally across the surfaces of the cylindrical guide rollers 17. In the nominal position, each data track is centered about its associated magnetic head as the tape travels longitudinally along the tape path. As the track density is increased, it becomes increasingly important to maintain the data tracks in their nominal position in alignment with the magnetic heads. Because of the close track-to-track spacing and narrow track width, a slight deviation of the data tracks from their nominal positions can cause errors in reading or writing information.
It is also desirable to maintain the magnetic tape along a predetermined path for the purpose of winding the tape onto a reel. One problem encountered in winding the tape onto the reel is that the edges of the tape have a tendency to rub against the flanges of the reel thereby causing the edges to chafe which will reduce the useful life of the tape.
One guidance system in a magnetic recorder/player for maintaining a tape along its nominal path makes use of cylindrical guide rollers with edge flanges at their ends to forcibly constrain the tape along its predetermined path. A problem encountered in this system is that the edges of the tape deteriorate over time as a result of friction against the edge flanges, thus requiring tape replacement. While this does not necessarily present a problem where this system is applied in a ground station, it certainly presents a problem where such a system is designed for application in a space satellite where it must operate over many years without maintenance.
Another guidance system for maintaining a tape along a nominal path makes use of crown guide rollers in place of the cylindrical guide rollers 17 shown in FIG. 1. Referring to FIG. 2, a crown guide roller 21 has a circumferential surface 22 that is convex in the axial direction. As the tape which is wrapped around the crown guide roller is travelling longitudinally, due to the convex surface 22, the crown guide roller has a tendency to center the tape without the need to use end flanges at the ends of the roller. While the crown guide roller is capable of reducing some deviation of the tape from its nominal path, it is not suitable for application in cases where there is a high frequency perturbation of the tape from its nominal path and where there is a sudden large perturbation. Also, it is difficult to precisely fix the lateral position of the crown guide roller to correspond to the desired nominal tape position.
Another automatic tape tracking system is disclosed in U.S. Pat. No. 4,582,235, issued to Gordon R. Schulz, the inventor of the present invention. The system disclosed therein is a relatively complex system employing cylindrical guide rollers and optical means for monitoring the position of the tape. The guide rollers are adjustable in height and to change the direction of their axes. Adjustments in the height and axial orientation of the rollers are made in response to the monitored position in order to maintain the tape in a desired location. This system is very useful for wide tape, e.g., two inches. However, the system is relatively complex, large and requires a relatively large amount of power.